Magnetic DC-to-DC converter

ABSTRACT

Magnetic direct current to direct current converter with the input isolated from the output. A pulse generator from the feedback is incorporated in the feedback circuitry to regulate the output relative to the input.

.Iadd.This is a continuation of application Ser. No. 08/430,168 filedApr. 27, 1998, and now abandoned, which was a continuation ofapplication 08/240,378, filed on May. 10, 1994, and now abandoned, andis a reissue of 07/462/100, filed Jan. 8, 1990 which issued as U.S. Pat.No. 5,113,333.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to power supplies and more particularly toa magnetic direct current to direct current converter having magneticcoupling feedback.

2. Description of the Prior Art

Converters typically switch an unidirectional source of current at ahigh frequency through transformer windings. An output winding of thetransformer provides an alternating current which may be rectified toproduce a d.c. source of power. A forward converter may include a switchwhich switches current through a transformer winding. An output windingprovides the alternating current in response alternatively to build-upand collapse of flux of the transformer.

There are many electrical power applications with dc-to-dc convertersrequiring power to be supplied at a particular voltage or current level.Many power supplies convert the input power to output power at thedesired current or voltage level. However, frequently, the input poweris unregulated such that the output current or voltage varies. Also, theload conditions on the power supply may vary which in turn impacts theoutput current and/or voltage. Furthermore, the temperature at which thecircuit is operating impacts the output current and/or voltage.

To maintain the power supply at a predetermined level, many powersupplies have a regulator which monitors the output and modifies theinput as necessary. Also, many applications require isolation of theoutput from the input. For example, it may be necessary to isolate theoutput side from noise existing on the input side. In switch-mode powersupplies having a transformer, the input circuit is frequentlyelectrically isolated from the output circuit, with a transistor switchin the input circuit tied to the primary coil and which is controlled bya feedback signal from the secondary coil. Electrical isolation betweenthe primary and secondary coils may also be maintained by anopto-isolator which transmits the feedback information from thesecondary coil side to the primary coil side. However, the linearity ofopto-isolators commonly varies with temperature, with a dramaticdecrease in gain at high temperature (above 85° C.) and a permanentdecrease over time. Also, the performance of opto-isolators is subjectto radiation. The gain varies as a function of such radiation.Consequently, opto-isolators are generally precluded from military andsatellite applications or other applications where the temperaturevaries significantly; long life is desired; and/or there are significantvariations in radiation.

Magnetic isolation is a further form of isolation and uses a transformeror inductor sampling method of feedback. The benefits are relativelyconstant performance notwithstanding temperature and time variations.The disadvantages include complexity, low performance due to signalaveraging, errors and noise feedback mixing with the desired signal.

The prior art includes U.S. Pat. No. 4,683,528, issued to Snow, et al.relating to a pulse position modulated regulation for power supplies.The circuitry includes a pulse transformer to transmit pulses from thesecondary coil side of the transformer to the primary coil side with thepower through the primary coil being controlled by varying the dutycycle of the drive signal for a transistor switch. U.S. Pat. No.4,357,654, issued to Ikenoue, et al. discloses an inductively coupleddc-to-dc converter. The circuitry includes an inductance for storingenergy when a switching transistor is turned on and releasing the storedenergy when the switching transistor is turned off, and a semiconductoractive element used as a flywheel element to provide the path forcurrent resulting from the stored energy. U.S. Pat. No. 4,355,353,issued to Michael Farrer discloses a power supply apparatus having atransformer reset sensing circuit to inhibit reset of a switchingtransistor in the primary side of a transformer until resetting of thetransformer.

SUMMARY OF THE PRESENT INVENTION

It is an object of the present invention to provide a magnetic feedbackwith magnetic isolation and of which the feedback circuitry is accurateand relatively uncomplicated in design.

It is a further object of the present invention to provide a magneticfeedback in which the output is highly regulated relative to the input.

It is a further object of the present invention to provide a magneticfeedback circuit of which the performance is relatively insensitive toambient temperature.

It is a further object of the present invention to provide a magneticfeedback circuit which is relatively insensitive to time of use.

It is a further object of the present invention to provide a magneticfeedback circuit which is relatively insensitive to radiation.

An exemplary embodiment of the present invention includes a magneticfeedback implemented in a dc-to-dc converter with a feedback coupledinductor connected to the load-side of a power transformer and with adiode to detect the feedback voltage during "flyback" of the powertransformer. The magnitude of the feedback is determined by the turnsratio and does not react to changes in temperature, age or radiation. Asampling switch circuit is in series with the diode to smooth andrecover the feedback signal. The sampling switch is regulated by asampling pulse. The timing of the sampling pulse is delayed and thewidth may be set to eliminate the switching energy and noise componentsto increase the load range.

An advantage of the magnetic feedback of the present invention is thatit is of relatively uncomplicated design.

Another advantage of the magnetic feedback of the present invention isthat the output is highly regulated relative to the input.

Another advantage of the magnetic feedback of the present invention isthat it has a long life.

Another advantage of the magnetic feedback of the present invention isthat it is operable over a wide temperature range.

These and other objects and advantages of the present invention will nodoubt become obvious to those of ordinary skill in the art after havingread the following detailed description of the preferred embodimentwhich are illustrated in the various drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a feedback circuit of the presentinvention implemented in a dc-to-dc converter;

FIG. 2 is a timing diagram of signals illustrating operation of theembodiment of FIG. 1 under moderate load conditions;

FIG. 3 is a timing diagram of signals illustrating operation of theembodiment of FIG. 1 under very light load conditions;

FIG. 4 is a schematic diagram of an alternative embodiment of thepresent invention; and

FIG. 5 is a timing diagram of signals illustrating operation of theembodiment of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic diagram of a magnetic feedback circuit of thepresent invention implemented in a dc-to-dc converter and referred to bythe general reference character 10. The converter includes a transformer12 having a primary winding 14 and a secondary winding 16. The primarywinding 14 has a center tap connected to a direct current supply source18 (V_(sp)) which is also joined to the ground reference of the primaryside of transformer 12. The supply source 18 may be of various forms andmay vary from a very low voltage to a very large voltage source. Suchapplications may include a battery, a generator on an aircraft, etc. Oneside of the primary winding 14 is joined to an electronic switch 20which also extends to ground and the other side of winding 14 is joinedto an electronic switch 22 which extends to ground. The switches 20 and22 may be in the form of pulse transistors such as power MOSFETS orbipolar transistors. The secondary winding 16 of the transformer 12 hasone end tied to a diode 24 and the other end tied to a diode 26 of whichthe cathodes are tied in common at a junction 27. The center tap of thewinding 16 extends to the load 28. In series with the diode 24 and theload 28 is a filter including an output filter inductor 30 wound on acore 32 and a filter capacitor 34 extending across the load 28. One sideof the load 28, capacitor 34 and the center tap of winding 16 are tiedto ground reference on the load side of transformer 12.

A feedback circuit network 35 is incorporated to sense the outputvoltage of the converter 10 and transfer it back to the primary side ofthe transformer 12. The network 35 includes a winding 34 which ismagnetically coupled to the winding 30 on the same common core 32. Thewinding 34 is grounded to the ground of the primary side of thetransformer 12. In series with the winding 34 is a diode 36, the cathodeof which is tied to a current regulating diode 37 which extends to theprimary side ground. The cathode of the diode 36 is also tied to asampling switch 38 which has one terminal extending to a capacitor 39which is grounded to the primary side ground. The sampling switch 38 maytake the form of a MOSFET switch with the gate tied to a sampling switchdriver 40.

The sampling switch 38 and sampling switch driver 40 are also tied to aprimary control circuit 41. The circuit 41 includes an error amplifier42 with one terminal tied to switch 38, another input terminal tied to areference potential V_(Ref), and an output terminal extending to a pulsewidth modulator 45. The output of the modulator 45 is joined to a pairof inverters 46 and 47. Inverter 46 is joined to switch 20 and tosampling switch driver 40. Inverter 47 is joined to switch 22 and tosampling switch driver 40.

The converter 10 may include a plurality of loads. For illustrativepurposes, the circuit of FIG. 1 is shown with two loads. For the secondload, there is a secondary winding 50 having a center tap and withopposite ends tied to a diode 52 and 54, respectively. The cathodes ofthe diodes 52 and 54 are joined in common to a filter inductor 56 whichis wound on the core 32. This inductor 56 is tied in series with a load58 which is also tied to the load-side return and in parallel with acapacitor 60.

In operation, and referring to FIGS. 1 and 2, the dc supply source 18provides a voltage V_(sp) which is applied to the transformer 12 at thecenterpoint primary winding 14. The number of windings on the primary 14to the center tap are represented as N_(p). The switches 20 and 22 ofthe primary control circuit 41 create open and close operations of theprimary winding circuit responsive to signals at the gates of theswitches 20 and 22. Accordingly, the magnetic flux in the coil 14decreases and increases responsive to the pulses V_(s) controlling theswitches 20 and 22 so as to create a magnetic coupling to the secondarywindings on the transformer 12. Viewing the secondary winding 16, thenumber of windings on the secondary 16 to the center tap are representedas N_(s1). The diodes 24 and 26 on the secondary windings 16 limit thecurrent flow to be unidirectional so as to provide pulses. The voltageV₁ at the junction 27 is a function of the turns ratio and the voltagedrop across the diodes 24 and 26. The current flow to the filter throughthe output inductor winding 30 creates magnetic flux in the winding 30and a voltage V_(L1) across said winding. The magnetic flux is in turnmagnetically coupled to the feedback winding 34. The number of windingson the inductors 30 and 34 are represented as N_(L1) and N_(FBK),respectively. The relative polarity of the windings 30 and the winding34 are opposite. A voltage V_(F2) is then provided across the input toone terminal of the switch 38 and the primary ground reference. Themagnitude of V_(F2) is a function of the potential across the winding 34and the drop across the diode 36. The diode 36 detects the voltage onthe feedback winding 34 during the time of flyback. The voltage dropdeveloped across the diode 36 is referred to as V_(DFBK). Asillustrated, the signal V_(F2) includes decaying perturbations at theleading edge and then flattens. This results in "noise" at the edges ofthe signals. Thus, it is desired to preclude such "noise" from feedbackto the primary control circuit 41. Accordingly, the gate 38 iscontrolled to remain open during the noise by delaying the outputsampling signal V_(SMP) of the switch driver 40 to the gate of switch 38by a time period T_(d) as shown in FIG. 2. Then, with the gate 38closed, the signal "V_(F3) " across the capacitor 39 is provided to oneterminal of the error amplifier 42 which compares it to the referencepotential V_(Ref). The output of said error amplifier 42 is then fed tothe pulse width modulator 45, i.e., including a sawtooth generator andcomparator. The pulse width modulator 45, then provides pulses of thecorrect pulse width through the inverters 46 and 47 to the switches 20and 22 and to the driver 40 to close the loop. Accordingly, the switches20 and 22 are closed in response to the feedback signals. The switches20 and 22 are connected in push-pull such that when one is closed, theother is open. Also, the sampling switch driver 40 provides the delayedpulse signal "V_(SMP) " to the gate of the sampling switch 40 inresponse to the feedback.

As shown by FIG. 2, for loads 28 wherein the output current I_(o) equalsor exceeds fifty percent of the ripple current of the inductor 30, thegate to the sampling switch 38 is not closed during the time periodT_(d) so as to avoid passing the leading edge perturbations of theV_(F2) potential to the primary control circuit 41. By incorporating thedelay T_(d), the perturbations are dissipated by the time that the gate38 is closed such that the potential V_(F3) is relatively flat. Thistends to prevent spikes and discontinuities contained in the feedbacksignal V_(F2) from appearing at the error amplifier input, V_(F3)thereby providing a highly regulated dc output.

In the situation wherein the application requires a very light load,e.g., output load current I_(o) is less than fifty percent of theinductor ripple current of the inductor 30, the signal waveforms becomeas illustrated in FIG. 3. As illustrated, the trailing edge on thesecond half of the V_(t) potential tends to build up at an irregularrate thereby adding further perturbations into the half-wave signalsV_(F2). Thus, the half-wave signal V_(F2), has perturbations at both itsleading and trailing edges. Accordingly, to avoid the perturbations atboth edges, the sampling switch driver 40 is such that it delaysconduction by the time period "T_(d) " and then only conducts for aperiod "T₁ " so as to avoid the perturbations at both ends of the"V_(F2) " signal. Consequently, the potential "V_(F3) " is relativelyflat.

To illustrate the effects of the conduction period of the samplingswitch 38, if the driver 40 is not controlled and merely delayed underthe very light load conditions, the waveforms V_(SMP) and V_(F3) in FIG.3 include in broken lines (for one cycle) of the wave shapes. Asillustrated, the potential V_(F3) would have a significant decreaseduring the trailing edge perturbations. Thus, for very light loads,without a fixed sampling time, regulation would be sacrified.

Though the discussion has concentrated merely on one load, namely load28, the same analysis applies for each load for applications withmultiple loads.

Accordingly, as is illustrated by the network of FIG. 1, the primaryside of the dc-to-dc magnetic converter is isolated from the secondaryside and the feedback winding is grounded on the primary side ground.Also, by utilizing the sampling switch driver 40 to drive the samplingswitch 38 with a delayed gate signal pulse, with moderate or largeloads, tends to eliminate the spikes which are present at the leadingedge of the feedback signal. Furthermore, by controlling both the delayand the width of the gate signal "V_(SMP) ", and thus the time frameduring which the sampling switch 38 is closed, during the half-wavefeedback signal "V_(F2) " perturbations at each end are elminated fromaffecting the regulation of the converter output. The end result is anoutput dc voltage V_(o) which is highly regulated and which remainsstable. Also, the transfer characteristics are primarily determined bythe turns ratio of the filter inductor 30 and the feedback inductor 34.Such ratio is insensitive to temperature, time and radiation. Mostapplications deem a load regulation of plus or minus two percent forload variations. With the time delay of the pulse V_(SMP) suchregulation is realized with a five to one load current variation. Withthe delayed fixed-time pulse V_(SMP), such regulation is realized with aten to one load current variation.

The voltage regulation is also a function of (a) the resistance of thewinding of the filter inductor 30; and (b) the voltage drop across thediodes 24, 26 and 36. These can be overcome by using larger wires toreduce the resistance in the windings and by selecting diodes havingsmaller voltage variations for the desired current range.

With the present invention the temperature coefficients of the outputvoltages are determined by; (1) the difference between the temperaturecoefficients of the diodes; and (2) winding resistance. To illustrate,using the load 28 for illustrative purposes:

    V.sub.L1 =V.sub.01 +VD+I.sub.o R.sub.1                     (1)

where,

V_(D) =V_(D1A) =V_(D1B) ;

R_(S) =winding resistance of coil 30; and

I_(o) =output current. ##EQU1## where N is number of turns on winding.Therefore, ##EQU2##

Thus, by selecting the appropriate terms ratio and the current densityof the diode 36 (set by I_(F)), the temperature coefficient can be madevirtually zero. Even if the temperature coefficient is not eliminated,it is well-defined as shown in equation (5) and if necessary, it can befurther compensated by introducing a temperature compensated correctionfactor to offset it.

With the turns ratio of the secondary winding to the filter inductorwinding the same for all sections, ##EQU3## the dynamic crossregulation, i.e., the variations in the loads across the varioussections, is very good. This is due to the fact that the feedback istaken from the unified and normalized output voltage. Also, the delayedsampling switch 38 not only eliminates the switching spikes, but alsowith I_(F), provides for a very fast discharge path. This improves thetransient response of the converter 10.

FIG. 4 illustrates an alternative embodiment of the present inventionand referred to the general reference character 68. Those componentssimilar to components of FIG. 1 carry the same reference numeraldistinguished by a prime designation. In FIG. 4, the converter 68includes a magnetic pulse feedback circuit 70. The circuit 70 includes atransformer with three coupled windings 71, 72 and 73 wound on a gappedcore 74. The winding 73, with turns N₃, has one end joined to thesecondary ground reference and the other end tied in series with a diode76 extending to the load 28'. The winding 72, with turns N₂, is tied tothe primary ground and to a trigger pulse generator 78 which extends tothe pulse width modulator 45'. The winding 71, with turns N₁, extendsfrom the primary ground reference to the diode 36'.

Assuming the turns ratio N₁ :N₂ :N₃ =1:1:1, then the timing diagram ofFIG. 5 illustrates the waveforms (2) of the signal of winding 72, thewaveform (1) of the signal winding 71, and V_(F3').

The voltage (2) across the winding 72 equals that across winding 73 suchthat

    V.sub.2 =V.sub.01 +V.sub.DSMP                              (6)

where V_(DSMP) is the voltage drop across the diode 76. Also, thevoltage (1) across the winding 71 equals in magnitude that across thewinding 72 such that, ##EQU4## The temperature coefficient of the outputvoltage can be made very small by tightly thermally coupling the diodes76 and 36', e.g., placed on the same hybrid substrate and using the sametype of diode for both. Also, since a gapped core can be used, thecharacteristics, e.g., winding inductance, interwinding capacitance, Q,etc., of circuit 70 are well defined. Thus, their values can be wellcontrolled which in turn limits temperature variations.

Continuous monitoring of the output voltage V₀₁ is available because thefeedback signal is always present. This is true even if the output is inthe fault conditions, e.g., short circuited, overloaded, etc. Also, thetransmitting of the feedback signal is fully synchronized with thesystem clock. This eliminates the possibility of generating an unstableduty cycle which in turn could generate random (or beat frequency)voltage ripple at the output. As can be seen, the feedback circuit 70only includes one active device, i.e., the diode 76. This allows theentire converter to be included on a single integrated circuit. Also,the transformer on the core 74 can be very small since it merely carriesa signal and does not carry any load current or high voltages. Thus, thecircuit 70 does not carry any significant quantity of power.

Although the present invention has been described in terms of thepresently preferred embodiment(s), it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alterations andmodifications will no doubt become apparent to those skilled in the artafter having read the above disclosure. Accordingly, it is intended thatthe appended claims be interpreted as covering all alterations andmodifications as fall within the true spirit and scope of the invention.

I claim:
 1. A direct current to direct current converter comprising, incombination:a power transformer with a primary winding and a secondarywinding, said primary winding having a first connection means forreceiving a direct current supply source and a second connection meansfor connection to a first ground reference, and said secondary windingbeing connected to a second ground reference; a primary control circuitincluding a switching means connected to said primary winding forcontrolling the duty cycle of power delivered to said primary windingfrom said source, and a comparator means for receiving and comparing areference signal and a feedback signal and generating an error signalrelative to a comparison and in turn generating responsive controlsignals to said switching means; and a feedback network including afirst inductive means connected to sense . .a.!. .Iadd.an.Iaddend.electrical load connected to said secondary winding, a feedbackinductor .Iadd.for generating a feedback signal and.Iaddend.magnetically coupled to said first inductive means, said firstinductive means connected in series with a first unidirectionalconductive valve and a second unidirectional conductive valve, saidfirst and second unidirectional conductive valves being connected toopposing ends of said secondary winding, said feedback inductorconnected in series with a third unidirectional conductive valve, asampling switch connected to said third unidirectional conductive ..gate.!. .Iadd.valve .Iaddend.and to said comparator means to controlcurrent flow intermediate said third unidirectional conductive ..gate.!. .Iadd.valve .Iaddend.and said comparator means, said samplingswitch including a control gate for controlling conduction through saidsampling switch, and gate control means connected to said gate and tothe primary control circuit to control said sampling switch responsiveto the status of said error signal .Iadd.for sampling said feedbacksignal during a steady state portion of said feedback signal.Iaddend..2. The converter of claim 1 wherein, said first inductive means and saidfeedback inductor are windings on a common core in transformerrelationship, the turns ratio of said first inductive means and feedbackinductor being one.
 3. The converter of claim . .1.!. .Iadd.4.Iaddend.wherein, said first and second unidirectional conductive valvesare diodes of which the . .matching.!. electrical characteristics are.Iadd.substantially .Iaddend.equal.
 4. A direct current to directcurrent converter comprising, in combination:a power transformer with aprimary winding and a secondary winding, said primary winding having afirst connection means for receiving a direct current supply source anda second connection means for connection to a first ground reference,and said secondary winding being connected to a second ground reference;a primary control circuit including a switching means connected to saidprimary winding for controlling the duty cycle of power delivered tosaid primary winding from said source, and a comparator means forreceiving a reference signal and a feedback signal and generating anerror signal relative to the comparison and in turn generatingresponsive control signals to said switching means; and a feedbacknetwork to sense an electrical load connected to said secondary winding,the feedback network including a first inductive means and a feedbackinductor magnetically coupled to said first inductive means, said firstinductive means .Iadd.being .Iaddend.connected in series with a firstunidirectional conductive valve . .and a second unidirectionalconductive valve, said first and second unidirectional valves beingconnected to opposing ends of said secondary winding.!., said feedbackinductor connected in series with a . .third.!. .Iadd.second.Iaddend.unidirectional conductive valve, a sampling switch connected tosaid . .third.!. .Iadd.second .Iaddend.unidirectional conductive ..gate.!. .Iadd.valve .Iaddend.and to said comparator means to controlcurrent flow intermediate said . .third.!. .Iadd.second.Iaddend.unidirectional conductive . .gate.!. .Iadd.valve .Iaddend.andsaid comparator means, said sampling switch including a control gate forcontrolling conduction through said sampling switch, . .gate.!..Iadd.inductive .Iaddend.control means . .connected to said gate and tothe primary control circuit to control said sampling switch responsiveto the status of said error signal.!., and a second inductive meansmagnetically coupled to said first inductive means and to said feedbackinductor, said second inductive means and feedback inductor beingconnected to said first ground reference, and said second inductivemeans being connected to said . .gate.!. .Iadd.inductive.Iaddend.control means.
 5. The converter of claim 4 wherein,said firstinductive means, second inductive means and feedback inductor are allwound on a common core; said first .Iadd.inductive means .Iaddend.andsaid feedback .Iadd.inductor having .Iaddend.winding.Iadd.s which.Iaddend.are wound with the same polarity and opposite to that of said ..feedback inductor.!. .Iadd.second inductive means.Iaddend..
 6. Theconverter of claim 5 wherein,said . .gate.!. .Iadd.inductive.Iaddend.control means is a trigger pulse generator.
 7. The converter ofclaim 5 wherein,said first inductive means, second inductive means andfeedback inductor are wound on a gapped core . .with said secondinductive means being placed within said gap.!..
 8. The converter ofclaim 7 wherein, the turns ratio of said first inductive means, secondinductive means and feedback inductor is one. . .
 9. The converter ofclaim 8 wherein,the polarity of said first inductive means and feedbackinductor are the same and opposite respectively to the polarity of saidsecond inductive means..!.
 10. A direct current to direct currentconverter comprising, in combination:a power transformer with a primarywinding and a secondary winding, said primary winding having a firstconnection means for receiving a direct current supply source and asecond connection means for connection to a first ground reference, andsaid secondary winding being connected to a second ground reference; aswitching means connected to said primary winding for controlling theduty cycle of power delivered to said primary winding from said source;a first unidirectional control valve connected to a first end of saidsecondary winding and in series with a first inductive means forconnection to an electrical load; a second unidirectional control valveconnected to a second end of said secondary winding and in series withsaid first inductive means; a feedback signal generating means forgenerating a feedback signal representative of output voltage of theconverter and including a second inductive means .Iadd.for generating afeedback signal .Iaddend.magnetically coupled to said first inductivemeans, said second inductive means being connected between said firstground reference and a third unidirectional control valve, and a voltagestorage means connected between said . .third.!. .Iadd.second.Iaddend.inductive means and said first ground reference whereby afeedback potential may be generated across said voltage storage means; adifferential amplifier means connected to said voltage storage means andto receive a select reference voltage for comparing a select referencevoltage to a . .signal.!. .Iadd.feedback .Iaddend.potentialrepresentative of said feedback . .potential.!. .Iadd.signal.Iaddend.; asampling driver means connected to receive a signal representative ofthe output of the differential amplifier means and for generating adelayed pulse signal representative of the output of the differentialamplifier means with said pulse signal delayed a select time perioddependent on a waveform of said feedback potential .Iadd.to sample saidfeedback signal during a steady state period of said feedbacksignal.Iaddend.; and a sampling switch means connected to the samplingdriver means, the differential . .driver.!. .Iadd.amplifier.Iaddend.means and to said third unidirectional control valve, wherebysaid feedback . .signal.!. .Iadd.potential .Iaddend.representative ofsaid feedback . .potential.!. .Iadd.signal .Iaddend.is controlledresponsive to said delayed pulse signal.
 11. The converter of claim 10wherein,said first inductive means and said second inductive means arewindings on a common core in transformer relationship, the turns ratioof said first and second inductive means being one. . .12. The converterof claim 11 wherein, the first unidirectional control valve and saidsecond unidirectional control valve are diodes of which the matchingelectrical characteristics are equal..!.13. The converter of claim ..12.!. .Iadd.11 .Iaddend.wherein,the . .polarity.!. .Iadd.polarities.Iaddend.of said first and second inductive means are . .the.!. oppositerelative to each other.
 14. The converter of claim 13 wherein,thesampling switch means is in the form of a three terminal electronicswitch having a gate connected to the sampling driver means forreceiving said delayed pulse signal.
 15. In an electronic transformercircuit wherein a primary winding of the circuit is connected to a firstground reference and a secondary winding is connected to a second groundreference and including a primary control circuit for controllingconduction of the primary winding, the improvement comprising:a feedbacknetwork to sense an electrical load connected to said secondary winding,the feedback network including a first inductor connected in series witha first unidirectional conductive valve and a second unidirectionalconductive valve, said first and second unidirectional conductive valvesbeing connected to opposing ends of said secondary winding, a feedbackinductor connected to said first ground reference and magneticallycoupled to said first inductor and connected in series with a thirdunidirectional conductive valve, a sampling switch having one terminalconnected with said third unidirectional conductive valve, said samplingswitch including a gate for controlling conduction through said samplingswitch of signals through said . .second.!. .Iadd.third.Iaddend.unidirectional conductive valve and means connecting saidsampling switch with said primary winding; and gate control meansconnected to said gate and to said primary control circuit to controlconduction of said sampling switch as a function of the conduction ofsaid primary winding.Iadd., for sampling said feedback signal during asteady state period of said feedback signal.Iaddend..
 16. An electronictransformer circuit of claim 15 wherein,said first inductor and saidfeedback inductor are windings on a common core in transformerrelationship, the turns ratio of said first inductor and said feedbackinductor being one.
 17. An electronic transformer circuit of claim ..16.!. .Iadd.18 .Iaddend.wherein,said first and second unidirectionalconductive valves are diodes of which the . .matching.!. electrical ..characters.!. .Iadd.characteristics .Iaddend.are .Iadd.substantially.Iaddend.equal.
 18. In an electronic transformer circuit wherein aprimary winding of the circuit is connected to a first ground referenceand a secondary winding is connected to a second ground reference andincluding a primary control circuit for controlling conduction of theprimary winding, the improvement comprising:a feedback network to sensean electrical load connected to said secondary winding, the feedbacknetwork including a first inductor connected in series with a firstunidirectional conductive valve . .and a second unidirectionalconductive valve, said first and second unidirectional conductive valvesbeing diodes connected to opposing ends of said secondary winding and ofwhich the matching electrical characteristics are equal.!., a feedbackinductor .Iadd.for generating a feedback signal .Iaddend.connected tosaid first ground reference and magnetically coupled to said firstinductor and connected in series with a . .third.!. .Iadd.second.Iaddend.unidirectional conductive valve, said first inductor and saidfeedback inductor are windings on a common core in transformerrelationship . .with the turns ratio of said first inductor and saidfeedback inductor being one.!., a sampling switch having one terminalconnected with said . .third.!. .Iadd.second .Iaddend.unidirectionalconductive valve, said sampling switch including a gate for controllingconduction through said sampling switch of signals through said ..third.!. .Iadd.second .Iaddend.unidirectional conductive valve andmeans connecting said sampling switch with said primary winding, ..gate.!. .Iadd.inductive .Iaddend.control means . .connected to saidgate and to said primary control circuit to control conduction of saidsampling switch.!. .Iadd.to control the generation of said feedbacksignal .Iaddend.as a function of the conduction of said . .primarywinding.!. .Iadd.first inductor.Iaddend., a second inductor magneticallycoupled to said first inductor and to said feedback inductor, saidsecond and feedback inductors being connected to said first groundreference and said second inductor being connected to said . .gate.!..Iadd.inductive .Iaddend.control means. .Iadd.19. A power supply havingan input including a return terminal such as a ground, a direct currentoutput having a return terminal such as a ground, the return terminalsbeing isolated from each other, and a feedback regulating circuitcoupled between the output and input for regulating the transfer ofpower between the input and output while preserving said isolation, thefeedback regulating circuit comprising:(1) a control circuit forcontrolling the transfer of power; and (2) a regulating circuitincluding:(a) a monitoring circuit responsive to said power supplyoutput and having a clamping characteristic; (b) a feedback circuitinductively coupled to said monitoring circuit for supplying a signalindicative of the output condition to said control circuit; and (c) atrigger circuit for initiating a magnetic transient in the couplingbetween said monitoring circuit and said feedback circuit; whereby acorrecting signal is applied to the control circuit. .Iaddend..Iadd.20.The power supply of claim 19 including a power transformer connectedbetween said input and output and wherein said control circuit comprisesa pulse width modulator for controlling conduction in the primary ofsaid transformer. .Iaddend..Iadd.21. The power supply of claim 19 orclaim 20 wherein said monitoring circuit receives a signal which is afunction of said power supply output. .Iaddend..Iadd.22. The powersupply of claim 19 or claim 20 including a source of reference signaland wherein said correcting signal is combined with said referencesignal to form an error signal for controlling said control circuit..Iaddend..Iadd.23. The power supply of claim 19 or claim 20 wherein saidtrigger circuit supplies a pulse to an inductor for initiating saidmagnetic transient. .Iaddend..Iadd.24. A power supply as defined inclaim 19 or claim 20 wherein said feedback circuit includes aninductance magnetically coupled to said monitoring circuit..Iaddend..Iadd.25. A power supply as defined in claim 19 or claim 20wherein said monitoring circuit includes an inductance clamped by asignal which is a function of said power supply output..Iaddend..Iadd.26. The power supply of claim 19 or claim 20 wherein saidmonitoring circuit and said feedback circuit each include at least onediode, the diode characteristics being substantially equal..Iaddend..Iadd.27. The power supply of claim 19 or claim 20 wherein saidmonitoring circuit and said feedback circuit each include inductive anddiode characteristics, the diode characteristics being substantiallyequal. .Iaddend..Iadd.28. A method of converting a DC signal to a DCsignal in a power supply, comprising the steps of:(A) supplying directcurrent to a power supply having (1) an input including a returnterminal such as a ground, (2) a direct current output including areturn terminal such as a ground, said return terminals being isolatedfrom each other, (3) a control circuit having an input coupled to saidpower supply output, and (4) a power controller connected between theoutput of said control circuit and said power supply input; (B)regulating the transfer of power between said input power supply andoutput while preserving said isolation, by applying a clamped correctingsignal derived from said output to said control circuit; and (C)initiating a magnetic transient in the control circuit to produce aregulating action in said power controller which is responsive to saidclamped correcting signal. .Iaddend..Iadd.29. The method of claim 28including a power transformer connected between said input and outputand wherein said power controller comprises a pulse width modulator forcontrolling conduction in the primary of said transformer..Iaddend..Iadd.30. The method of claim 28 or claim 29 wherein saidclamped correcting signal which is a function of said power supplyoutput. .Iaddend..Iadd.31. The method of claim 28 or claim 29 includinga source of reference signal and wherein said clamped correcting signalis combined with said reference signal to form an error signal forcontrolling said power controller. .Iaddend..Iadd.32. The method ofclaim 28 or claim 29 wherein said magnetic transient is initiated by atrigger circuit in said control circuit supplying a pulse to aninductor. .Iaddend..Iadd.33. The method of claim 28 or claim 29 whereinsaid control circuit includes an inductance magnetically coupled to amonitoring circuit. .Iaddend..Iadd.34. The method of claim 33 whereinsaid monitoring circuit includes an inductance clamped by a signal whichis a function of said power supply output. .Iaddend..Iadd.35. The methodof claim 34 wherein said monitoring circuit and said control circuiteach include at least one diode, the diode characteristics beingsubstantially equal. .Iaddend..Iadd.36. The method of claim 34 whereinsaid monitoring circuit and said control circuit each include inductiveand diode characteristics, the diode characteristics being substantiallyequal. .Iaddend.